We use new millimeter wavelength observations to reveal the important effects that giant (parsec-scale) outflows from young stars have on their surroundings. We find that giant outflows have the potential to disrupt their host cloud, and/or drive turbulence there. In addition, our study confirms that episodicity and a time-varying ejection axis are common characteristics of giant outflows.

We carried out our study by mapping, in great detail, the surrounding molecular gas and parent cloud of two giant Herbig-Haro (HH) flows; HH 300 and HH 315. Our study shows that these giant HH flows have been able to entrain large amounts of molecular gas, as the molecular outflows they have produced have masses of 4 to 7 solar –which is approximately 5 to 10% of the total quiescent gas mass in their parent clouds. These outflows have injected substantial amounts of momentum and kinetic energy on their parent cloud, in the order of 10 solar masses km/sec and 1044 erg, respectively. We find that both molecular outflows have energies comparable to their parent clouds' turbulent and gravitationally binding energies. In addition, these outflows have been able to redistribute large amounts of their surrounding medium-density (n ~ 103 cm-3) gas, thereby sculpting their parent cloud and affecting its density and velocity distribution at distances as large as 1 to 1.5 pc from the outflow source.

Our study, in combination with other outflow studies, indicate that a single giant molecular outflow in a molecular cloud of less than about 80 solar masses has the potential to seriously disrupt its parent cloud. We, therefore, conclude that the cumulative action of many giant outflows will certainly have a profound effect on their cloud's evolution and fate.

Our detail study of the outflow morphology, velocity structure, and momentum distribution –among other properties of both outflows– lead us to suggest that they are predominantly formed by bow-shock prompt entrainment, from an episodic wind with a time-varying axis. Close to the outflow source of HH 315, though, the coexistence of a jet-like wind and a wide-angle wind explains better the observed outflow properties.